But it was in rural Pennsylvania, southeast of Pittsburgh, that Mr. Silman earned a national reputation. There, Wright designed Fallingwater, one of the most breathtaking houses of the 20th century, for the Pittsburgh merchant Edgar J. Kaufmann and his wife, Liliane.
Fallingwater seems to erupt from the forest around it, with terraced slabs jutting up to 14½ feet — seemingly without support — over a waterfall in the Bear Run creek. The daring cantilevered design conferred celebrity status on Wright after its completion in 1937.
Frank Lloyd Wright’s Fallingwater, southeast of Pittsburgh. Mr. Sillman was ultimately called in to prevent the home’s cantilevered reinforced concrete balconies from collapsing, employing what was called an “elegant” solution.CreditTory Struck/Silman
Even before that, however, Kaufmann wondered whether Wright had specified enough steel reinforcing bars in the concrete beams of the main cantilever. Wright resented the questioning, but Kaufmann saw to it that extra reinforcing bars were installed anyway.
Ultimately, that precaution was not enough. “In the mid-1990s we heard from an engineering student that his research showed Fallingwater might be in structural trouble,” Lynda S. Waggoner, the director emerita of Fallingwater, said in an email on Monday.
“According to his calculations, the cantilevers were under-engineered and in danger of failure,” she continued. Ms. Waggoner telephoned Mr. Silman. “After what seemed like minutes but was likely seconds, he responded, ‘I will have someone down there this week.’ ”
By then, one cantilevered slab was tilting about seven inches downwardfrom its original position, a condition known as deflection. Mr. Silman persuaded Fallingwater’s owner, the Western Pennsylvania Conservancy, to erect temporary steel shoring under the slab. In 2001, flagstone flooring and built-in furniture was removed from the slab to expose the concrete beams and perpendicular joists below.
Five cables — made of as many as 13 half-inch-diameter steel strands — were placed alongside three major beams, like tendons and bone, with six smaller cables placed alongside the joists. This steel network was anchored to the existing concrete piers under the house, then tautened to restore structural integrity to the cracked beams. (The operation has been likened to orthodontics.)
“Bob’s solution to the faltering cantilevers was elegant,” Ms. Waggoner said. “It preserved the material integrity of the building and minimized any incidental damage while preventing future deflections.”
The project, lasting six months, “ensured Fallingwater’s ability to continue to amaze visitors from the world over for generations to come,” she said.